As known, the majority of internal combustion engines are turbocharged. A turbocharger is a forced induction device used to allow more power to be produced for an engine of a given size. The benefit of a turbocharger (or simply turbo) is that it compresses a greater mass of intake air into the combustion chamber, thereby resulting in increased power and/or efficiency. Turbochargers are commonly used on truck, car, train and construction equipment engines. They are popularly used with Otto cycle and Diesel cycle internal combustion engines and have also been found useful in automotive fuel cells.
The boost pressure, which is the maximum pressure the compressed intake air will get under the different engine operating conditions, is a key parameter, since that its accurate estimation avoids integrator wind up of torque and/or boost controller. The integrator is necessary to avoid deviations from boost or respectively torque set-point. If there is an error the integrator winds up until the error is zero. These values are considered in the adaptation. For example, more boost pressure is needed to get the desired torque at high altitude. The boost pressure the compressor is able to provide depends on the energy provided to the turbine. If there is no energy at the turbine, the compressor is not able to provide more boost pressure and the error keeps increasing. In that case the integrator would wind up and the adaptation would learn wrong values. Using these values going back to sea level would lead to over boost.
Furthermore, the accurate estimation of the boost pressure optimizes the interaction between boost pressure and torque control and provides reliable maximum torque estimation considering the ambient conditions and the enthalpy at the turbine.
Finally, the accurate estimation of the boost pressure optimizes the down shift behavior for both automatic and manual transmissions. In fact, being possible to estimate the boost pressure for current conditions and for different engine speeds, the algorithm is calculating the energy provided to the turbine and based on that, the maximum boost pressure. If the maximum boost pressure is lower than the desired boost pressure, the mass flow to the turbine has to be increased, by increasing the engine speed done by a down shift. For automatic transmission, it is also important to know the maximum available torque to perform an upshift. Therefore it is also possible to avoid “hunting” or “toggling” between several gears.
Up to now, no method of estimating the boost pressure is available. Therefore a need exists for a method of estimating the boost pressure the turbocharger can provide to the engine, with a reliable accuracy and without a very complex and time consuming routine.